Forested Buffer Strips Research Articles

The effects of land‐use change on semi‐aquatic bugs (Gerromorpha, Hemiptera) in rainforest streams in Sabah, Malaysia

Abstract Land‐use change and agricultural expansion have caused marked biodiversity loss in Southeast Asia, but impacts on freshwater communities have been very little studied. Semi‐aquatic bugs are abundant in streams, provide prey for many other animals, and are sensitive to environmental change, making them a relevant group for studying land‐use change. We investigated the effects of logging and conversion of forest to oil palm plantations on semi‐aquatic bugs in Sabah, Malaysia, and the potential value of retaining riparian buffer strips in plantations, by sampling across 12 rivers along an existing land‐use gradient. We recorded catchment, riparian, and stream‐scale environmental variables and surveyed semi‐aquatic bugs within streams in old‐growth forest, logged forest, and oil palm plantation with (OPB) and without buffer strips (OP). We recorded the abundance, richness, total biomass, and proportion of juveniles and winged adult individuals of all species, together with the sex ratio of a common morphospecies (Ptilomera sp.), as possible indicators of disturbance effects. Average abundance and average richness, but not total biomass, of all semi‐aquatic bugs were lower in areas with higher habitat disturbance. In particular, average abundance in old‐growth forest was more than two, four, and six times higher than that in logged forest, OPB, and OP, respectively. Average richness in old‐growth forest was higher than in logged forest by two species, but more than two and three times higher than in OPB and OP, respectively. The presence of riparian buffer strips in oil palm had little effect on the abundance and richness of semi‐aquatic bugs. We found no significant differences in the proportion of juveniles, winged adult individuals, or the sex ratio of Ptilomera sp. along the disturbance gradient. In conclusion, oil palm plantations were associated with lower average abundance and richness of semi‐aquatic bugs than forest sites, but community composition did not differ markedly between logged and old‐growth forests. We also found that the forested buffer strips maintained within our oil palm plantation study sites did not protect forest species of semi‐aquatic bugs. Maintaining forest may therefore provide the best option for the conservation of semi‐aquatic bugs, but further studies of the effects of land‐use change and management options are needed across Southeast Asia.

The effect of buffer strip width and selective logging on streamside polypore communities

Preserving streamside forest habitats or buffer strips is considered to reduce forestry-related biodiversity loss in commercial forest landscapes. However, it is still unclear what type of management in and near streamside forests can be undertaken without compromising their biodiversity and natural change through succession. Using a before–after, control–impact study design, we tested the impacts of forested buffer strips (15 or 30 m wide, with or without selective logging), preserved after clear-cutting, on the changes of polypore communities in streamside boreal forests in Finland. Manipulations in 28 sites produced four treatment classes, the community compositions of which were compared with seven unmanaged controls before and 12 years after the manipulations. The polypore community composition in 15 m wide buffer strips changed differently than that in controls and resembled the community composition typically found in production forests. Moreover, selective logging tended to homogenize polypore communities. These responses of polypore communities indicate that the natural biodiversity and succession of streamside forests was disturbed in both 15 m wide and selectively logged buffer strips. Streamside forests in nonlogged 30 m wide buffer strips seemed to retain the natural polypore community composition and succession, at least during the 12-year period.

The effect of buffer strip width and selective logging on riparian forest microclimate

Riparian forests have cool and humid microclimates, and one aim of leaving forested buffer strips between clear-cut areas and streams is to conserve these microclimatic conditions. We used an experimental study set up of 35 streamside sites to study the impacts of buffer strip width (15 or 30 m) and selective logging within the buffer strips on summer-time air temperature, relative air humidity and canopy openness 12 years after logging. The buffer strip treatments were compared to unlogged control sites. We found that 15-meter buffer strips with or without selective logging and 30-meter buffer strips with selective logging were insufficient in maintaining temperature, relative humidity and canopy openness at similar levels than they were in control sites. In contrast, 30-meter buffer strips differed only little from control sites, although they did have significantly lower mean air humidity. Microclimatic changes were increased by southern or southwestern aspect of the clear-cut, and by logging on the opposite side of the stream. We also tested how the cover of three indicator mosses (Hylocomium splendens, Pseudobryum cinclidioides and Polytrichum commune) had changed (from pre-logging to 12 years post-logging) in relation to post-logging air temperature, relative air humidity and canopy openness. We found that each of the species responded to at least one of these physical conditions. Air humidity was the most significant variable for explaining changes in the cover of the indicator moss species, suggesting that the changes in this microclimatic component has biological impacts. We conclude that to preserve riparian microclimatic conditions and species dependent on those, buffer strips should exceed 30 m in width, and not be selectively logged. Wider buffer strips are required if the clear-cut is towards south or southwest, or if the two sides of the stream are logged at the same time or during subsequent years.

Do large carnivores use riparian zones? Ecological implications for forest management

As part of forest management guidelines, most North American jurisdictions require the preservation of forested areas adjacent to streams and rivers (i.e. riparian zones). Forested buffer strips with restrictions on timber harvest and road-building (i.e. riparian buffer zones) were originally implemented to protect aquatic functions and resources. Riparian buffer zones now also target terrestrial habitats and wildlife. Even so, forestry managers who implement guidelines seldom consider the value of riparian zones (RZs) for large carnivores, partly due to a lack of data available. In the present study, our objective was to understand the role of riparian zones and riparian buffer zones for large carnivores in managed boreal forests. We used nine years of GPS telemetry data (2007–2015) from radio collared grizzly bears (Ursus arctos) in the Kakwa region of west-central Alberta, Canada to quantify both the use (i.e. the amount of time grizzly bears spend in RZs) and selection (i.e. use in relation to the available riparian habitat) of RZs. We examined the effects of season, sex, distance class (0–30 or 30–60m from streams and rivers), and the surrounding forest (harvested versus non-harvested) on use and selection of RZs. We found grizzly bears spent 19.1% of their time within 60meters from streams and rivers. Selection of RZs declined relative to the distance from streams and rivers (10.8% within 0–30m and 8.4% within 30–60m). During summer, grizzly bears selected RZs in harvested areas and avoided them in non-harvested areas. There was no difference in selection of RZs in harvested areas between males and females; however, in non-harvested areas, females avoided RZs and selected RZs less compared to males. These results, particularly the selection of RZs in harvested areas where RZs consist mostly of riparian buffer zones, suggest that riparian buffers provide valuable grizzly bear habitat in multiple-use landscapes. Forest management practices can support grizzly bear habitat conservation efforts by implementing riparian buffer zones in identified grizzly bear habitat and considering grizzly bear habitat use of RZs and riparian buffers as one component of riparian zone management.

Riparian Partial Harvesting and Upland Clear Cutting Alter Bird Communities in a Boreal Mixedwood Forest

Forested buffer strips are typically prescribed around water bodies during forest harvesting operations to minimize effects on aquatic communities and to maintain fish and wildlife habitat. It has been argued that the systematic application of these buffer strips in the boreal forest results in the creation of an unnatural distribution of linear patterns of older-growth forest which is not consistent with the current emulating natural disturbance paradigm. We conducted a multi-year, temporally and spatially controlled, manipulative experiment to investigate the short-term impacts of an alternative practice of riparian partial harvesting and upland clear cutting on breeding and migrating forest birds. Effects on breeding bird community composition were assessed using a modified point counting method. Effects of harvesting on habitat utilization during fall migration were assessed by mist-netting. Breeding bird communities changed significantly post-harvest, but riparian communities diverged less from the pre-harvest condition than upland communities. Populations of early successional/edge species increased post-harvest and forest dependent species declined. Population declines tended to be smaller in the riparian partial cuts than in the upland clear cuts. Capture rates and movement patterns of fall migrants were unaffected by riparian partial harvesting, but catches of Tennessee Warbler (Oreothlypis peregrina), Nashville Warbler (Oreothlypis ruficapilla), Palm Warbler (Setophaga palmarum) and Yellow-rumped Warbler (Setophaga coronata) increased in upland clear cuts. Our results suggest that partial harvesting in riparian reserves may be a viable management option that accommodates the needs of forest dependent birds.

Response of water yield function of ecosystem to land use change in Nansi Lake Basin based on CLUE-S model and InVEST model .

Land use change has an important role in hydrological processes and utilization of water resources, and is the main driving force of water yield function of ecosystem. This paper analyzed the change of land use from 1990 to 2013 in Nansi Lake Basin, Shandong Province. The future land use in 2030 was also predicted and simulated by CLUE-S model. Based on land use scenarios, we analyzed the influence of land use change on ecosystem function of water yield in nearly 25 years through InVEST water yield model and spatial mapping. The results showed that the area of construction land increased by 3.5% in 2013 because of burgeoning urbanization process, but farmland area decreased by 2.4% which was conversed to construction land mostly. The simulated result of InVEST model suggested that water yield level of whole basin decreased firstly and increased subsequently during last 25 years and peaked at 232.1 mm in 2013. The construction land area would increase by 6.7% in 2030 based on the land use scenarios of fast urbanization, which would lead to a remarkable growth for water yield and risk of flowing flooding. However, the water yield level of whole basin would decrease by 1.2 % in 2013 if 300 meter-wide forest buffer strips around Nansi Lake were built up.

Riparian reserves within oil palm plantations conserve logged forest leaf litter ant communities and maintain associated scavenging rates.

Summary The expansion of oil palm plantations at the expense of tropical forests is causing declines in many species and altering ecosystem functions. Maintaining forest‐dependent species and processes in these landscapes may therefore limit the negative impacts of this economically important industry. Protecting riparian vegetation may be one such opportunity; forest buffer strips are commonly protected for hydrological reasons, but can also conserve functionally important taxa and the processes they support.We surveyed leaf litter ant communities within oil palm‐dominated landscapes in Sabah, Malaysia, using protein baits. As the scavenging activity of ants influences important ecological characteristics such as nutrient cycling and soil structure, we quantified species‐specific rates of bait removal to examine how this process may change across land uses and establish which changes in community structure underlie observed shifts in activity.Riparian reserves had similar ant species richness, community composition and scavenging rates to nearby continuous logged forest. Reserve width and vegetation structure did not affect ant species richness significantly. However, the number of foraging individuals decreased with increasing reserve width, and scavenging rate increased with vegetation complexity.Oil palm ant communities were characterized by significantly lower species richness than logged forest and riparian reserves and also by altered community composition and reduced scavenging rates.Reduced scavenging activity in oil palm was not explained by a reduction in ant species richness, nor by replacement of forest ant species by those with lower per species scavenging rates. There was also no significant effect of land use on the scavenging activity of the forest species that persisted in oil palm. Rather, changes in scavenging activity were best explained by a reduction in the mean rate of bait removal per individual ant across all species in the community. Synthesis and applications. Our results suggest that riparian reserves are comparable to areas of logged forest in terms of ant community composition and ant‐mediated scavenging. Hence, in addition to protecting large continuous areas of primary and logged forest, maintaining riparian reserves is a successful strategy for conserving leaf litter ants and their scavenging activities in tropical agricultural landscapes.

AVIAN NEST SURVIVAL IN COASTAL FORESTED BUFFER STRIPS ON PRINCE OF WALES ISLAND, ALASKA

Abstract In an effort to provide wildlife habitat and link blocks of forested habitat, coastal forested buffer strips in the Pacific Northwest are managed to mitigate effects of fragmentation that result from timber harvesting adjacent to a coastline. We examined the effect of coastal forest buffer strip width on avian nest survival on Prince of Wales Island, Alaska, in 2003 and 2004. We established nest monitoring plots in two buffer width treatments, narrow ( 350 m, n = 3), and monitored a total of 142 nests of six species: the Pacific-slope Flycatcher (Empidonax difficilis), Chestnut-backed Chickadee (Poecile rufescens), Winter Wren (Troglodytes troglodytes), Swainson's Thrush (Catharus ustulatus), Hermit Thrush (Catharus guttatus), and Varied Thrush (Ixoreus naevius). We modeled and compared the daily survival rate (DSR) of each species in both buffer width treatments. Point estimates for DSRs were slightly higher within wide buffers, but confidence intervals overlapped for al...

Forested Buffer Strips and Breeding Bird Communities in Southeast Alaska

Abstract: Forested buffer strips are used to mitigate fragmentation and habitat loss and are a common feature in management of riparian landscapes. Low‐elevation, old‐growth coastal forests are a rare riparian habitat that can benefit from similar conservation measures. We evaluated the effectiveness of postlogging, forested buffer strips for forest‐dwelling birds in the coastal temperate rainforest of southeast Alaska, USA. Our objective was to compare bird composition and density among forested buffer strips of differing widths and controls at the stand and landscape scales. We applied a 2‐stage sampling design stratified by forested buffer width and randomly selected 24 managed and 18 control sites to sample over 2 breeding seasons. We estimated abundance of birds using the paired‐observer, variable‐circular plot method. We modeled combined effects of buffer width and vegetation and landscape characteristics on bird density at 2 spatial scales. Species richness and diversity were greatest in the narrowest buffers, but species composition in the largest buffers (≥400 m) was most similar to that in control blocks. Abundance of 3 of 10 common species differed across forested buffer treatments and controls. Densities of red‐breasted sapsucker (Sphyrapicus ruber) and Pacific‐slope flycatcher (Empidonax difficilis) were positively related to buffer width, whereas density of ruby‐crowned kinglet (Regulus calendula) was negatively associated with buffer width. Parameter estimates for buffer width effects at both spatial scales were similar within species. We found few habitat and landscape variables that clearly affected density of our focal species, and among species no predictor variables affected density in a similar fashion. We recommend retaining forested buffers ≥400 m to support composition and abundance of forest‐dwelling birds, particularly those species that rely on interior forest conditions. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):674‐681; 2008)

Effects of forest harvesting on Bufflehead and Common Loon foraging behavior

We compared foraging behavior of Bufflehead (Bucephala albeola Linnaeus) and Common Loon (Gavia immer Brünnich) on eight lakes in harvested and unharvested boreal mixedwood forest in northern Alberta, Canada. For one summer before (1996) and two summers after (1997, 1998) forest harvesting around three of the eight lakes, we recorded the duration of Bufflehead and Common Loon dives. After logging, forested buffer strips 100 m-wide separated cut-blocks from lakes (‘harvested lakes’). ‘Unharvested lakes’ were surrounded by ⩾450 m of undisturbed forest throughout the study. There were no detectable differences in dive duration between harvested and unharvested lakes for Bufflehead or Common Loon. Correlations between environmental variables (water clarity, fish biomass, depth) and the duration of Common Loon dives were not significant. However, the duration of Bufflehead dives differed between lakes, unrelated to forest harvesting. The duration of Buffle-head dives was negatively correlated with water clarity but was not significantly correlated with fish biomass. While our study shows that the foraging behavior of Buffle-heads was affected by lake conditions, the utility of aquatic birds as indicators of the effects of forestry on western boreal lakes remains unproven.

SUBSTRATE FORM DETERMINES THE FATE OF BRYOPHYTES IN RIPARIAN BUFFER STRIPS

Studies on the effectiveness of forest buffer strips left along streams after logging have long overlooked the biota of the buffers themselves, despite their high species richness. We investigated mosses and liverworts (bryophytes), abundant and species‐rich groups in boreal forests, before and 2.5 years after logging along 15 small streams. In each site, two 1000‐m2 (20 × 50 m) plots along the stream were inventoried; one plot in an area subjected to clear‐cutting, and another in a buffer strip (10 m wide on each side of the stream). Ten plots along small streams in forest reserves in the same region were used as references. We found that less than half as many bryophyte species per plot disappeared after logging in the buffer strips compared to the clearcuts. The changes in bryophyte cover and in species composition were smaller in the buffer strips, and the species that were negatively affected in the clearcuts were less affected in the buffer strips. However, there was a significant change in species composition in the buffer strips compared to the references. Substrate form and taxonomic group were important factors in understanding this turnover. Many species growing on substrates with a convex form (e.g., logs, tree bases, and mesic ground) decreased or disappeared, while species on concave substrates were rather unaffected. This held for both mosses and liverworts, although liverworts were generally more sensitive than mosses. The difference in response of assemblages on convex vs. concave substrates makes changes in microclimate due to logging a likely explanation. The species in most need of protection (i.e., the red‐listed species) were among the ones with strongest declines in the 20 m wide buffer strips. In order to function optimally for bryophyte conservation, forests along small streams need to be protected from high windthrow frequency and strong edge effects. Increasing the width of buffer strips at sites with known or potential values (e.g., large amounts of woody debris or boulders) should be considered a better strategy than using narrow buffer strips with a fixed width.

Abundance and species composition of amphibians, small mammals, and songbirds in riparian forest buffer strips of varying widths in the boreal mixedwood of Alberta

Forested buffer strips are left along water bodies after forest harvesting to protect water quality and fish stocks, but little is known about their utility as reserves for forest species in managed landscapes. We report on changes in terrestrial vertebrate communities from pre- to post-harvest in experimentally created buffer strips (20, 100, 200, and 800 m wide) in a boreal mixedwood forest in Alberta, Canada. We trapped anuran amphibians and small mammals and spot-mapped bird territories around 12 lakes (4 treatment levels, 3 replicates) before and after harvesting. Changes in small mammal or amphibian abundance were not detected for any treatment relative to controls; however, these species are habitat generalists that used and even bred in clearcuts. Total bird abundance did not change after harvesting, with the exception of crowding in 20-m buffers 1 year post-harvest. Species composition did not change for amphibians and small mammals after harvest, but forest-dependent bird species declined as buffer width narrowed from 200 to 100 m and narrower. We concluded that 20–100 m buffers would not serve as reserves for forest songbirds in managed landscapes, but that 200 m wide strips conserved the pre-harvest passerine bird community, at least up to 3 years post-harvest.

Forest Buffer Strips: Mapping the Water Quality Benefits

Abstract Forest buffer strips are widely recommended for trapping nonpoint-source pollutants and protecting surface water quality, yet few models are designed to identify key areas for buffer installation and management. This article presents a conceptual model of polluted runoff dynamics to provide traction in estimating watershed-wide forest buffer needs. Inputs required for these estimates include elevation and land-cover maps, along with derived products that represent basic nutrient runoff principles.

Riparian forests in the Oregon Coast Range

We examined the structure and composition of forested buffer strips in the central and northern Coast Range of Oregon and found little botanical evidence of an effect on plant community composition or dynamics from isolating these forests as buffers. Thus, concerns about microenvironmental changes due to extended edge effects appear unfounded in this region for the plant community. Tree stocking was low, especially on terraces; evidence suggests that competition, as well as site conditions, limit the regeneration of trees, including conifers. Understory diversity (richness) was greater under conifer canopy types; understory cover was greater under hardwood canopy types. Tree regeneration, especially on terraces and under hardwoods, was limited although more abundant than in older, unmanaged riparian forest. In the long term, succession models for this region suggest that many of these riparian areas will succeed to a largely treeless community.

Breeding Bird Response to Riparian Buffer Width in Managed Pacific Northwest Douglas-Fir Forests

We examined the relative importance of riparian vs. upland habitats to breeding birds by comparing species abundance, richness, and similarity of bird communities in managed Douglas-fir forests in western Washington State, USA. We also examined whether forested buffer strips along second- and third-order streams effectively maintain the pre-logging riparian breeding bird community by comparing species abundance, richness, and turnover among three treatments: (1) unharvested controls; (2) sites that were clear-cut, leaving a narrow (∼14 m) forested buffer on both sides of the stream; and (3) sites that were clear-cut, leaving a wide (∼31 m) forested buffer along both sides of the stream. Deciduous trees, berry-producing shrubs, and other deciduous shrubs less common in adjacent upland forest characterized streamside zones. Despite different vegetation features, riparian and upland habitats did not differ in any measures of bird species richness and composition. No species or species group was more abundant in the upland. Neotropical migrants, resident species, and species associated with deciduous trees and shrubs in forested habitats were more abundant in riparian habitats than in adjacent uplands. Total bird abundance and abundance of four species (American Robin [Turdus migratorius], Pacific-slope Flycatcher [Empidonax difficilis], Black-throated Gray Warbler [Dendroica nigrescens], and Winter Wren [Troglodytes troglodytes]) were higher in riparian habitats. Abundance of these riparian associates was correlated with percent cover of berry-producing shrubs and the number of deciduous trees in the canopy. We found that the number of breeding bird species on sites with narrow buffers increased from slightly fewer than controls before harvest to an average of 10 more species than controls after harvest, a change reflected in an average 20% increase in species turnover on narrow-buffer sites relative to controls. Total bird abundance did not differ between treatments and controls. Resident species, those species associated with shrubs in forested habitats and conifer trees, declined on both buffer treatments. Species associated with upland and riparian forests (Black-throated Gray Warbler, Golden-crowned Kinglet [Regulus satrapa], and Brown Creeper [Certhia americana]) decreased in abundance on riparian buffer treatments relative to controls, whereas species associated with open, shrubby habitats (Dark-eyed Junco [Junco hyemalis], Cedar Waxwing [Bombycilla cedrorum], and Song Sparrow [Melospiza melodia]) increased in abundance on one or both riparian buffer treatments. High species turnover on narrow-buffer treatments indicated that buffers <14 m on each side of the stream did not maintain the pre-logging bird community. There was little difference in species turnover or species richness between the wide-buffer treatment and the control, indicating that a 30-m buffer on both sides of second-order and third-order streams maintains most of the pre-logging bird community in the first two years postharvest. The Black-throated Gray Warbler was the only riparian associate to decline on both the narrow- and wide-buffer treatments; its abundance was positively correlated with buffer width, and a buffer ≥45 m wide on each side of second- and third-order streams was needed to support populations at densities found on unharvested controls. To maintain the entire breeding bird community associated with forested riparian habitats in the coastal Northwest, we recommend a minimum buffer of 45 m along both sides of second- and third-order streams. Habitat features such as deciduous trees (Alnus rubra and Acer macrophyllum) and berry-producing shrubs (especially Rubus spectabilis) appear to be important and should be maintained within forested riparian buffer strips. This study documents short-term effects of riparian treatments on the breeding bird community, which may take several years to respond to habitat manipulations. Thus, we recommend continued monitoring to assess long-term effects of buffer width reduction.

BREEDING BIRD RESPONSE TO RIPARIAN BUFFER WIDTH IN MANAGED PACIFIC NORTHWEST DOUGLAS-FIR FORESTS

We examined the relative importance of riparian vs. upland habitats to breeding birds by comparing species abundance, richness, and similarity of bird communities in managed Douglas-fir forests in western Washington State, USA. We also examined whether forested buffer strips along second- and third-order streams effectively maintain the pre-logging riparian breeding bird community by comparing species abundance, richness, and turnover among three treatments: (1) unharvested controls; (2) sites that were clear-cut, leaving a narrow (∼14 m) forested buffer on both sides of the stream; and (3) sites that were clear-cut, leaving a wide (∼31 m) forested buffer along both sides of the stream. Deciduous trees, berry-producing shrubs, and other deciduous shrubs less common in adjacent upland forest characterized streamside zones. Despite different vegetation features, riparian and upland habitats did not differ in any measures of bird species richness and composition. No species or species group was more abundant...

Playing with Asimina triloba (pawpaw): a species to consider when enhancing riparian forest buffer systems with non-timber products

A dynamic model that depicts the growth, production and possible economical gains from Asimina triloba (pawpaw), a native North American fruit, is presented. Very few horticultural data exists on this species, calibration can only be done based on estimates and on educated ecological sense. This fruit was selected to be modeled because it is native to the Eastern US and because very little is known about it. Perhaps, with the construction of a model some insight on its productivity can be obtained. The interest in this fruit stems from a deeper problem. As a consequence of the increased pollution in the Chesapeake Bay Watershed, different actions have been taken in order to control and restore its environment. Among such actions, the building and maintenance of riparian forest buffer strips has been suggested and enforced. Farmers have been adamant about implementing these new approaches because land would have to be taken out of production, thus incurring an economic loss. However, if the riparian forest buffer is enhanced with economically viable non timber species, profit could be made from the land. The authors suggest the use of pawpaws as one of many options to include in the harvestable zone of the riparian forest buffer system. Three biological scenarios and four economical scenarios were tested in the model. We observed that unless pawpaw harvesting associated wages are cut, or subsidies for the economical exploitation of pawpaw riparian buffer strips are generous, the financial viability of such buffer strips using pawpaw as the harvestable species is reduced. In one of such scenarios, given a 5 ha pawpaw riparian buffer strip, where the farmer pays no wages, the pawpaw fruit is sold at $0.99 each, and the buffer is planted from new, the net present value of the buffer strip is $26 396.60.

EVALUATION OF POTENTIAL GROSS INCOME FROM NON-TIMBER PRODUCTS IN A MODEL RIPARIAN FOREST FOR THE CHESAPEAKE BAY WATERSHED

The creation of riparian forest buffer zones for water quality management in agricultural landscapes takes land out of production, incurring an economic loss for the landowner. However, planting and harvesting techniques, such as those employed in indigenous systems of tropical agroforestry, can enhance riparian forest buffer strips with economically viable species. This kind of riparian forest buffer can be harvested and generate income from otherwise unproductive tracts of land. This practice would make the implementation of riparian forest buffers more acceptable to farmers, by generating income while helping to improve water quality. The present project provides an economic model for the harvest of non-timber products (fruits, nuts and ornamentals) from riparian forest buffer zones in the Chesapeake Bay region. Potential gross income from harvest is calculated to demonstrate the feasibility of this strategy. Given certain assumptions, the gross income can amount to $60,934.30/ha/year.

FOREST PRACTICES AS NONPOINT SOURCES OF POLLUTION IN NORTH AMERICA1

ABSTRACT: Forest management activities may substantially alter the quality of water draining forests, and are regulated as nonpoint sources of pollution. Important impacts have been documented, in some cases, for undesirable changes in stream temperature and concentrations of dissolved oxygen, nitrate‐N, and suspended sediments. We present a comprehensive summary of North American studies that have examined the impacts of forest practices on each of these parameters of water quality. In most cases, retention of forested buffer strips along streams prevents unacceptable increases in stream temperatures. Current practices do not typically involve addition of large quantities of fine organic material to streams, and depletion of streamwater oxygen is not a problem; however, sedimentation of gravel streambeds may reduce oxygen diffusion into spawning beds in some cases. Concentrations of nitrate‐N typically increase substantially after forest harvesting and fertilization, but only a few cases have resulted in concentrations approaching the drinking‐water standard of 10 mg of nitrate‐NIL. Road construction and harvesting increase suspended sediment concentrations in streamwater, with highly variable results among regions in North America. The use of best management practices usually prevents unacceptable increases in sediment concentrations, but exceptionally large responses (especially in relation to intense storms) are not unusual.

Riparian vegetated buffer strips in water‐quality restoration and stream management

SUMMARY A review is presented of the literature on riparian vegetated buffer strips (VBS) for use in stream‐water‐quality restoration and limitations associated with their use are discussed. The results are also presented of recent investigations on the effectiveness of a forested and a grass vegetated buffer strip for reducing shallow subsurface inputs of nutrients from agriculture to a stream in central Illinois, U.S.A. Because riparian zones link the stream with its terrestrial catchment, they can modify, incorporate, dilute, or concentrate substances before they enter a lotic system. In small to mid‐size streams forested riparian zones can moderate temperatures, reduce sediment inputs, provide important sources of organic matter, and stabilize stream banks. Several questions on the utility and efficiency of vegetated buffer strips for stream restoration still remain unanswered, including: what types (grass v forest) are most efficient; do they become nutrient saturated; are they only temporary sinks; how does species composition influence effectiveness; and, what is the optimal width of buffer to facilitate nutrient reduction under different conditions? Water samples were collected (1989–90) from lysimeters located at three depths (60, 120, and &gt; 120cm) in an upland area planted in conventional row crops (corn and soybean) and in three adjacent riparian buffer treatments, a 39m wide grass buffer. a 16 m wide mature forested buffer, and a buffer planted in row‐crops to the stream bank. Concentrations of dissolved and total phosphorus and nitrate‐N in each sample were determined following major precipitation events over a seventeen month period. Both the forested and grass VBS reduced nitrate‐N concentrations in shallow groundwater (up to 90% reduction). On an annual basis the forested VBS was more effective at reducing concentrations of nitrate‐N than was the grass VBS, but was less efficient at retaining total and dissolved P. During the dormant season, both grass and forested buffer strips released dissolved and total P to the groundwater. The VBS apparently acted as a nutrient sink for much of the year, but also released accumulated nutrients during the remaining portion of the year. Periodic harvesting of plant biomass may reduce the amount of P released during the dormant season. VBSs are not as effective in agriculture areas with tile drained fields. Alternative restoration practices such as discharging drain tiles into wetlands constructed parallel to the stream channel may prove to be a more effective means of controlling non‐point‐source agricultural inputs of nutrients in such areas.